Chemical nickel plating bath

ABSTRACT

A chemical nickel plating bath containing hydrazine or its salts for precipitating nickel coatings in a substrate and having catalytic or corrosion inhibiting properties.

United States Patent 1 1 Haack 1 Oct. 28, 1975 1 CHEMICAL NICKEL PLATING BATH 2.822.294 2/1'958 Gutzeit et a1. 106/1 x 1 2,916,401 12/1959 Puls 106/1 X [75] Inventor mack Bern, Germany 3,024,134 3/1962 Nixon et a1. 106/1 x [73] Assignee: Schering AG, Berlin and h ep er Bergkamen Germany 3,403,035 9/1968 Schneble et a1. 106/1 [22] Filed: Mar. 18, 1970 3,438,798 4/1969 Baudrand 106/1 X [21] Appl. No.2 20,828 OTHER PUBLICATIONS Schwartz, M.,Z Proc. Amer. Electroplating Society, [30] Foreign Application Priority Data Vol. 47 (1960), pp. 176-183.

Apr. 17, 1969 Germany 1920152 Primary ExamirierLorenzo B. Hayes [52] US. Cl 106/1; 117/47 A; 117/130 E; Atmrney, Agent, or Firm-Joseph F. Padlon 117/160 R [51] Int. Cl. C23C 3/02 7 T A [58] Field of Search 106/1; 117/130 E, 130, [5 ABS R CT 7/1 0 47 A A chemical nickel plating bath containing hydrazine or its salts for precipitating nickel coatings in a sub- 56] References Cited strate and having catalytic or corrosion inhibiting UNITED STATES PATENTS PmPemesll/l947 Pessel 106/1 X 1 Claim, No Drawings 1" CHEMICAL NICKEL PLATING BATH; 1

The invention relates to a chemical nickeljplatin'g bathcontaining hydrazine or its salts for precipitating nic'k'el coatings having corrosion inhibiting or catalytic properties. v V Nickel coatings can be deposited from known'baths by chemical reduction, thatis, without an externalcurrent source. These baths contain a nickel salt, a' reducing agent, cornplexfor'rning agentsand'other addition agents in the dissolved state, and they deposit nickelon als in this manner; but also many inactive' metals and even non-conduct'ors after' previous activation treat" ment, for example, with palladium nuclei.

The reduction of'nickelcompounds with sodiu m hy pophosphite has been known for the longest time. Depending on experimental conditions, the coatings so deposited contain 3 13% phosphorus. Theyihave the disadvantage of having a lower' melting'poi'rit' and a much smaller electric conductivity that pure nickel deposits. Also, they readily become passive and'are therefore difficult" to reinforceiiby' galvanic de position because the adherence of the galvanic face coating is low. Moreover, hypophosphite baths are'notistable and tend to decompose. It also: difficult to maintain the electrolyte for extended 'p eriodsbecause phosphite accumulates as a reaction product, and sparingly soluble nickel phosphite is precipitated. The suspended nickel phosphite causes rough coatings and'ultirr'iately decomposition of the bath.

It is further known thatnickel salts can bereduced by means of sodiumiborohydride and ofboiazanesJThe coatingsdeposited contain 5 7% boron addition to the nickel. However, it is n'oted'that theflow melting point and the small electrical conductivity of the nickel-boron alloys are disadvantages, Moreover, the nickel baths containing sodium borohydride can be regenerated only to a limited extent. Aborate which formed as a reaction product accumulates in the electrolyte, and interferes with nickel deposition. special disadvantage of sodium borohydride as a reducing gent is its rapid hydrolysis in the nickel bath Beeause this, reaction takes place independently from the nickel deposition, the yield of the reaction, based on sodium borohydride, decreases materially with the decreasing use of thebath. f j n '1' f A chemical nickel bath' containing a nickel salt," a complexing agent, buffering'icompounds, hydrazine or its derivatives, and optionally alkali metal hydroxide has been described, in U .S Pat. No. 3 ,l98,6'59.'The bath is operated at a value of 65 to 1 land at a, temperature of 7,0f to 100T, preferably 9 to 9 C ..Ammoniuin carbonate may be added to the bath asa'complexing agent and bnffering compound in'amounts of 0.01 or 0.02 mole per liter. There is no suggestion, however, thangreater aniounts of-this compound be used, nor that the pH value be increased beyond the indicated maximum limit. However, under the described conditions, the deposition rate of the nickel isvery low and the stability of the bathis unsatisfactory. Because the bath is operated at felativelyjhi gh temperatures, it is not well'suited to thenickel coating of plasties. 7

According to the invention, nickel matings; Lhaving corrosion inhibiting and/ or catalytic effects are obtained from a bath which a high deposition rate and by carbonates. i

is'ex-treinly' stable. 'As-the known bath, thefbath'of the invention contains 'anaquebus"solution" of nickel salt;

complexing agent,'hydrazin'e or' its salts,and optionally alkali metal hydroxide, as a "buffering'compound'; however'fa't least one 'waterisolubles alt of phosphoricacid or carbonic acid with-inorganicor organic bases in concentrations above 0.05 mole per liter, and'preferably between 0.05 and 1.0 mole/liter areiusedf and it has"a pl-lvalu'e higher thanll'. i v

A pH value which is higher than of'tl1'e known bath" and the higher concentratibn of the abovementioned buffering compounds in the bathof the invention as compared to the known bath provide substantial'advantages'and constitute a major'ad'van'ce in the art. T:

Corrosion resistant nickel coating s of great hardness can be deposited'with the bath of the invention on metals and on non-conductors. These'nickel layers do not tend to turn passive when theyare reinforced by galvanic deposition. M

It is also possible to produce nickel coatings having remarkable catalytic effects which are suitable particu-' larly as hydrogenation anddehydrog'enation catalysts.

They can, bedeposited on metalliesnrtaces of any desired shape and, inaddition to good adherence, have the advantage of not being pyrophoric. Thebath of the invention additionally permits, nickel to be deposited already at a. bath temperature above C. The deposition rate is, very high, and the stability of the bath isexcellent. The upkeep of the electrolyte thus .does not presen tany problems. .lt is another, significant advantage thatthe electrolyte canbe regenerated indefinitely with'suitable, concentrated stock solutions of the individual ingredients.

,Suitable watersoluble salts of phosphoric acid and carbonic acid include, for vexample,-.the sodium, potas;

sium, ammoniumand hydrazonium salts..

T he coatings deposited from the bath with the use 0 phosphates as buffering compounds generally. are, of better quality thanthe coatings obtained withthe use ofcarbonates. The stability of the bath and the nickel.

.improved by phosphates than depositionrate are more The concentration of the aforementioned phosphates and carbonatesisin the range above 0.05 mole/liter; preferably between 0.05 to 1 .0 mole/liter.-

' The aforementioned buffering-agents increase not of the bath, but have the additional advantage to achieve a better adjustment and maintenance of the optirnal pH value when used in the'aforernentioned con-. centratioris, than ispossible with the known system.

-. They "also cause high solubility ofi the nickel salts in the *l-lydrazine and its saltsjfor exarnple, hydrazine sulfate, are employedasreducing agents. The concentrad n er e reducing agent is about 0.01 to'4.0 moles/ liteflfbase'd'on the liydrafziriecontent;

Asis' wen known; nickel-salts canb'e held in solution w in an'alkaline medium only complexing agents. In

order to make the desired high deposition rate of nickel possible} enickelfcornplexs 'mustl'b'e ineit'lier too sta- Complexing agents particularly suitable for this purpose are, for example, ammonia, amino alcohols and the salts of diphosphoric acid, such as Na ,P O in concentrations of about 0.01 to 4.0 moles/liter.

It is possible to use ammonia as a complexing agent even at elevated temperatures regardless of its volatility when the electrolyte is suitable covered. The usual cover of floating solid bodies, however, is not sufficient. It has been found advantageous to cover the bath with an inert agent insoluble in the liquid of the bath. preferably an aliphatic or aromatic hydrocarbon. such as decalin, or an ether of low volatility, such as di-nbutyl ether.

Objects of metal or ceramics which are first moistened with water can be entered into the bath through the cover layer without the cover layer adhering to them. Organic synthetic resins, however, are generally wetted by the floating covering layer and can thereafter not be coated with nickel.

The bath of the invention is prepared in a manner known in itself, preferably, however, by mixing the components in the following sequence: water, nickel salt, complexing agent, phosphate or carbonate, hydrazine or its salt. Ultimately, the pH is adjusted to the desired value or more than 1 1 if necessary, for example, by addition of alkali metal hydroxides such as sodium hydroxide.

The bath of the invention may have the following composition: 0.01 to 0.5 mole/liter nickel salt, 0.01 to 4.0 moles/liter comlexing agent, 0.01 to 4.0 moles/liter hydrazine or a corresponding amount of a hydrazine salt, between 0.05 and 1.0 mole/liter of a water soluble salt of phosphoric or carbonic acid, and optionally up to 3 mole/liter alkali metal hydroxide, in aqueous solution.

The bath is used in a manner known in the art. Also, this bath is particularly well suited for nickel plating plastic surfaces.

The necessary pretreatment and activation of the plastic surfaces is carried out in the usual manner. Many organic synthetic resin compositions can be roughened by etching, for example, with hot chrome sulfuric acid. The etched plastics are subsequently dipped in a solution of a noble metal salt, for example, palladium chloride, and thereafter in a reducing agent, for example, hydrazine. The activated plastics are then rinsed, and subsequently nickel plated in the chemical nickel plating bath. A nickel plating bath containing a diphosphate, such as Na P O is particularly suitable for nickel plating organic synthetic resin compositions or plastics. Nickel is already deposited at the low bath temperature of over 50C.

At lower bath temperatures, however, the nickel deposition on plastic surfaces activated by means of palladium nuclei starts only after a fairly long induction period.

As has further been found, this induction period can be substantially shortened by the addition of a very small amount of alkali metal hypophosphite, such as sodium hypophosphite, to the nickel plating bath. Simultaneously, complete nickel coating of the plastics and good adhesion of the nickel deposits are achieved. The preferred concentration of the hypophosphite is in the range between approximately 0.002 and 0.1 mole/- liter.

According to the invention, hydrazine-bearing nickel baths are already stabilized and excellently by the addition of phosphates or carbonates. Further stabilization is possible by adding certain inhibitors in low concentrations. Particularly suitable inhibitors are the water soluble salts of lead, cadmium, bismuth, thallium or tin with inorganic or organic acids, or metal cyanides, preferably alkali metal cyanides, in preferred concentrations of 10' to 10 mole/liter.

According to a further embodiment of the invention, the bath may additionally contain water soluble salts of cobalt, germanium, tin or thallium in concentrations of about 10" to 10 mole/liter. Suitable salts are, for example, the chlorides and sulfates. The deposition conditions are analogous to those of nickel. The alloys obtained from the baths of this composition are distinguished by their superior catalytic activity.

The following Examples further describe and illustrate baths according to the invention.

EXAMPLE l 0.1 Mole/liter nickel (11) chloride 2.0 Mole/liter ammonia 0.4 Mole/liter hydrazine 10' Mole/liter lead (11) acetate as stabilizer 0.4 Mole/liter dipotassium hydrogen phosphate pH 12.6; adjusted with sodium hydroxide Cover layer: di-n-butyl ether Deposition rate: 3.7 um/hr at 50C Appearance of nickel layer: light brown, dull EXAMPLE 2 0.1 Mole/liter nickel (ll) chloride 3.0 Mole/liter ammonia 0.4 Mole/liter hydrazine 0.4 Mole/liter dipotassiumhydrogen phosphate 3X10 Mole/liter potassium cyanide as stabilizer pH 12.2; adjusted with sodium hydroxide Cover layer: decalin Deposition rate: 15.6 ,um/hr at C Appearance of nickel layer: dark brown, dull EXAMPLE 3 0.05 Mole/liter nickel (l1) sulfate "0.2 Mole/liter sodium diphosphate (Na P O 0.2 Mole/liter hydrazine 0.4 Mole/liter sodium carbonate 10' Mole/liter bismuth (111) nitrate as stabilizer pH 11.1

Deposition rate: 5.4 um/hr at 70C Appearance of nickel layer: gray, dull EXAMPLE 4 0.05 Mole/liter nickel (l1) sulfate 0.2 Mole/liter sodium diphosphate (Na P O 0.4 Mole/liter hydrazine 0.4 Mole/liter dipotassium hydrogen phosphate 10" Mole/liter potassium cyanide as stabilizer pH 11.1; adjusted with sodium hydroxide Deposition rate: 16.7 um/hr at C Appearance of nickel layer: brown, bright EXAMPLE 5 0.05 Mole/liter nickel (l1) sulfate 0.2 Mole/liter sodium diphosphate (Na P O 0.6 Mole/liter hydrazine 0.4 Mole/liter dipotassium hydrogen phosphate 10 Mole/liter tin (11) chloride as stabilizer pH 12.0; adjusted with sodium hydroxide Deposition rate: 7.6 um/hr at 70C Appearance of nickel layer: light, bright EXAMPLE 6 0.03 Mole/liter nickel (ll) sulfate 0.3 Mole/liter sodium diphosphate (Na P O 0.4 Mole/liter hydrazine 0.4 Mole/liter dipotassium hydrogen phosphate 0.008 Mole/liter sodium hypophosphite l Mole/liter cadmium (l1) sulfate as stabilizer pH 12.0; adjusted with sodium hydroxide Deposition rate: 3 um/hr at 60C Appearance of nickel layer: light, bright This electrolyte may also be used for nickel plating plastics.

EXAMPLE 7 0.05 Mole/liter nickel (ll) chloride 1.5 Mole/liter monoethanolamine 0.4 Mole/liter hydrazine 0.4 Mole/liter dipotassium hydrogen phosphate 3X10 Mole/liter thallium (l) sulfate pH 11.7; adjusted with sodium hydroxide Deposition rate: 8.0 um/hr at 70C Appearance of nickel layer: brown, semi-bright EXAMPLE 8 0.05 Mole/liter nickel (ll) sulfate 0.005 Mole/liter cobalt (ll) sulfate 0.2 Mole/liter hydrazine 0.4 Mole/liter dipotassium hydrogen phosphate 0.2 Mole/liter sodium diphosphate (Na P O From this electrolyte, when adjusted to pH 1 1.4 (with sodium hydroxide), and at a temperature of 70C, a coating was deposited on a steel sheet. This deposit is distinguished by remarkable catalytic activity.

The catalytic activity was determined by the rate of decomposition of hydrazine in a solution of the composition 0.1 mole/liter hydrazine 0.3 mole/liter disdoium hydrogen phosphate pH 12.1; adjusted with sodium hydroxide at 70C. The decomposition rate was found to be' 300 umole hydrazinelcm hr.

By way of comparison, the decomposition rate of the hydrazine under identical experimental conditions on a sheet of pure nickel (rolled) which was etched at 70C in 2 N hydrochloric acid was less than 3 umole hydrazine/cm hr.

EXAMPLE 9 From an electrolyte of the composition 0.05 mole/liter nickel (ll) sulfate 10 mole/liter thallium sulfate 0.6 mole/liter hydrazine 0.4 mole/liter dipotassium hydrogen phosphate 0.2 mole/liter sodium diphosphate (Na P O a catalytically active coating was deposited at pH 12.0 (adjusted with sodium hydroxide) and at 70C as described in Example 8.

The catalytic activity or the alloy coating was 310 umole hydrazinelcm hr.

EXAMPLE 10 From an electrolyte of the composition 0.05 mole/liter nickel (ll) sulfate 10 mole/liter tin (ll) chloride 0.4 mole/liter hydrazine 0.2 mole/liter sodium diphosphate (Na P O 0.4 mole/liter dipotassium hydrogen phosphate a catalytically active coating was deposited at pH 1 1.4 (adjusted with sodium hydroxide) and at 70C as described in Example 8.

The catalytic activity of the alloy coating was as follows:

390 umole hydrazine/cm hr.

What is claimed is:

1. in an alkaline chemical nickel plating bath having a surface layer of di-n-butyl ether and a pH above 1 1 comprising an aqueous solution of a nickel salt, a reducing agent selected from the group consisting of hydrazine and hydrazine salts, a complexing agent and a buffering agent, the improvement of which comprised from 0.05 to 1 mole per liter of at least one water soluble salt of an acid selected from the group consisting of amonium, sodium, potassium and hydrazonium salts of carbonic acid and phosphoric acid, said bath comprising about 10 to 10 moles per liter of at least one water soluble salt of a metal selected from the group consisting of cobalt, germanium, tin and thallium. 

1. IN AN ALKALINE CHEMICAL NICKEL PALATING BATH HAVING A SURFACE LAYER OF DI-N-BUTYL ETHER AND A PH ABOVE 11 COMPRISING AN AQUEOUS SOLUTION OF A NICKLE SALT, A REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE AND HYDRAZINE SALTS, A COMPLEXING AGENT AND A BUFFERING AGENT, THE IMPROVEMEMT OF WHICH COMPRISING FROM 0.05 TO 1 MOLE PER LITER OF AT LEAST ONE WATER SOLUBLFE SALT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF AMONIUM, SODIUM, POTASSIUM AND HYDRAZONIUM SALTS OF CARBONIC ACID AND PHOSPHORIC ACID, SAID BATH COMPRISING ABOUT 10**-4 TO 10**-2 MOLES PER LITER OF AT LEAST ONE WATER SOLU SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF COBALT, GERMANIUM, TIN AND THALLIUM. 